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"The object of this thesis is to determine by analytical methods the temperature at any time within a homogeneous semi-infinite solid protected by a uniform layer of insulation, while its one and only one plane face is subjected to a periodically fluctuating temperature. The temperature at an infinite distance within the solid is to remain constant, and the heat flow in the other two directions is to be considered negligible.

Periodically fluctuating temperatures are frequent in both nature and engineering. The surface of the earth is subjected to temperature changes which are very nearly periodic, and these changes are made possible by the sun in its daily and annual cycle. A knowledge of these temperature fluctuations is very helpful when a decision is to be made as to the depth at which water pipes must be laid to avoid the danger of freezing. In the engineering field the subject of periodic temperature changes has been given considerable attention. These changes must be considered in the construction of heat engines, annealing of castings, cooling of ingots, and the heating and cooling of slabs and furnace wall sections.

The study of heat conduction is not limited to problems of heat alone. In the field of fluid flow through a porous media, in certain gravitational problems, in elasticity, and in current and static electricity, the problems involved and equations used are, in most cases, analogous to problems of heat conduction.

This particular problem in periodic heat flow was chosen by the author because thus far all analytical treatment had been on the basis of heat flow taking place in a homogeneous material. It is the object of this paper to investigate the effects of a layer of insulation on periodic heat flow"--Introduction, pages 1-2.